A138598 Numbers k such that |2^(2*k-27)-27| is prime.

15, 16, 17, 23, 25, 305, 1277, 2675, 3179, 8987, 9013, 27493, 42703

Offset

1,1

Links

Table of n, a(n) for n=1..13.

Example

2^(2*17-27)-27=101, 2^(2*23-27)-27=524261, 2^(2*25-27)-27=8388581, ...

Mathematica

q=27; For[i=q, i<=q, a={}; Do[x=2^(2*n-i)-i; If[PrimeQ[x], AppendTo[a, n]], {n, 20^2}]; Print["2^(2*n-", i, ")-", i, " ", a]; i=i+2]
Select[Range[1000], PrimeQ[Abs[2^(2#-27)-27]]&] (* Harvey P. Dale, Nov 12 2015 *)

Prog

(PARI) is(n)=ispseudoprime(abs(2^(2*n-27)-27)) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Sequence in context: A214424 A358043 A090461 * A281879 A354626 A114841

Adjacent sequences: A138595 A138596 A138597 * A138599 A138600 A138601

Keyword

more,nonn

Author

Vladimir Joseph Stephan Orlovsky, May 13 2008

Extensions

a(7)-a(11) from Iain Fox, Jan 13 2018

a(12) from Iain Fox, Jan 16 2018

a(13) from Iain Fox, Jan 18 2018

Status

approved